In the field of liquid crystal displays (LCDs), substantial resources have been expended to provide bright screen displays having high-resolution and wide viewing angles. Generally, the brighter the LCD display, the higher the resolution, and the wider the viewing angle through which the display is visible, the better the display is considered to be. This is generally true, for example, in the fields of laptop computers and LCD televisions.
Much research has thus gone into developing bright, wide-angle, high-resolution LCD displays, such as the color displays found on laptop computers like the IBM CL57SX. These LCD displays are of excellent quality when measured against the desirable characteristics mentioned above. They also require significant amounts of power to function, yielding relatively short viewing times of about one hour when battery-powered for portable use.
Set out below are several examples of LCD displays including back-lighting systems selected to collimate light projected through the displays, making the displays more efficient.
U.S. Pat. No. 4,704,004 to Nosker shows a light box incorporating a reflector, a linear Fresnel lens, polarizers and a diffuser, for collimating light to uniformly illuminate a liquid crystal display. The collimated light is projected through the LCD display, and the diffuser is positioned as desired to widen the viewing angle.
U.S. Pat. No. 4,874,228 to Aho et al. shows a backlit display including a lens structured to reflect narrow-angle-incident light at 90.degree. to the angle of incidence. At least one light source is positioned to provide light at a narrow angle of incidence. This light is reflected at a 90.degree. angle, projecting an essentially collimated beam through an adjacent LCD display.
In contrast to systems utilizing uncollimated light, the patents described above to Nosker and Aho et al. utilize collimated back-lighting systems to improve the brightness and thus the efficiency of LCD displays. However, even these collimated back-lighting systems have substantial power requirements and limited battery time in portable operations.
In addition to limiting power consumption while maintaining screen brightness, in many applications it is desirable to provide a bright screen and high-resolution while providing a limited viewing area (i.e. a narrowed viewing angle). Such applications include those in which privacy is desirable, for example during the use of a data entry touch-screen such as an automatic teller machine (ATM) typically found at banks. Other uses include, for example, private operation of notebook computers in public areas, and private viewings of movies or other entertainment media in similarly public viewing places.